In the most extensive independent analysis of PG&E since the Sept. 9 San Bruno catastrophe, an expert panel’s report Thursday scathingly criticized the utility, finding “multiple weaknesses” in its natural gas-line operations and accusing the company of putting profits ahead of public safety.

“Frankly, this report is damning of PG&E almost across the board,” said Michael Peevey, president of the California Public Utilities Commission, which ordered the study. Vowing that the commission will act on many of its recommendations, he added, “all these things are extremely deep and disturbing.”

The five experts, whom the commission appointed shortly after the blast to scrutinize the agency and PG&E, reached a number of unsettling conclusions:

PG&E has been too heavily focused on its own financial performance and not nearly enough on insuring its pipes are safe. When the experts asked a top PG&E official what change “would most positively affect safety in the future,” their report said they were dismayed to hear that “the recovery of costs for safety improvements would be the most important factor.”

The company, once known as an innovator, began to lose its way in 2000 when it went through bankruptcy. After that, the report said, the company cut back its attendance at industry conferences and other events, which may have contributed to “an insular mindset” and diminished its “drive for continuous improvement.”

PG&E’s program for maintaining the structural integrity of its gas lines was faulted for “not identifying all threats, as required by regulation,” and not doing enough “to prevent or mitigate” those dangers.

The report also criticized PG&E’s much ballyhooed “Pipeline 2020 program,” which the company proposed to upgrade its pipeline system after the explosion, which killed eight people and destroyed 38 homes. “We did not find it to be well-reasoned or based on a thoughtful examination of alternatives,” the report said of the program, which also proposes adding automatic shut-off valves to many gas pipes.

In a stunning revelation, the panel — which hired several pipeline experts to help with its study — concluded that a defective weld in the seam of the San Bruno gas-line segment that burst probably was so weakened by the 2008 replacement of a sewer line that it later ruptured. The sewer work used a method that caused extreme shaking of the ground near the gas pipe.

The National Transportation Safety Board, which is investigating the accident, has not issued a final report on the cause. But it has interviewed PG&E officials and others about the sewer work.

The report also found fault with the commission. It said the agency’s staff wasn’t sufficiently trained, lacks enough people to adequately monitor natural gas pipelines and “admitted it was less effective in dealing with PG&E than with other utilities.”

Having more knowledgeable employees would be especially helpful now, it noted, as the agency tries to monitor the extensive and technically complicated water-pressure tests PG&E is conducting on its gas lines to check for leaks.

Instead of just trying to “check the boxes” when its inspectors review PG&E’s operations, the report said, the agency “must summon up the courage and resources to monitor” the utility more thoroughly.

PG&E, in a statement issued by Lee Cox, the company’s acting CEO and chairman, said it was “grateful” for the panel’s report.

“We will move quickly to review the report’s detailed findings and take further action to improve the safety, quality and performance of our gas system,” Cox said. “We need to make major improvements in our operations and culture in order to deliver the performance our customers rightly expect — and that we expect from ourselves.”

Mark Toney, executive director of The Utility Reform Network, a San Francisco consumer group, called the panel’s report “a regurgitation of what’s been in the press already,” and criticized the panel for conducting its inquiry “behind closed doors.”

But the study was applauded by members of the commission, including Peevey, who noted, “we seem to have drifted — both ourselves, this commission, and those we regulate — into something of a culture of complacency.”

Paul Clanon, the commission’s executive director, agreed that his agency in recent years had failed to spot obvious signs of trouble at PG&E, adding “it’s clear that didn’t work or we would not have had San Bruno.” He said the agency would seek to increase its budget and already is considering one change the report endorsed — letting its staff slap utilities with fines, a power that only the agency’s five appointed commissioners now have.

The commission already has demonstrated a tougher attitude toward PG&E. Besides launching an investigation of PG&E’s record-keeping practices, which could result in a multimillion-dollar fine against the company, the regulatory agency Thursday directed PG&E to pressure test or replace the roughly 600 to 700 miles of pipeline for which reliable records are not available.

PG&E, which estimates the cost of pressure testing a mile of pipeline at $150,000 to $500,000, already has begun testing 152 miles of its natural gas transmission lines. But the commission’s order dramatically increases the number of miles it will have to examine.

The expert panelists also questioned the need for the commission to spend its time overseeing mobile homes and propane gas systems, saying that responsibility detracts from its ability to supervise companies like PG&E.

Assemblyman Jerry Hill, D-San Mateo, agreed.

“Spending most of their time doing mobile home park gas inspections, maybe that’s not where their resources should be,” he said. But Hill said the state should look closely at the PUC’s budget before offering any funding increases, adding, “you have to look at their budget and see how they prioritize their expenses.”